Possible to Add Light?

So, I'm new to the forums and have a possibly interesting question. Is it possible to 'add' two 'rays' of light (which do not excite air, nor refract) from things such as lasers and have the result a point of intersection where the photons somehow are able to go off (brightly) in many directions, creating a point of visible light? (sorry for the run on sentence)

No - light beams at sensible powers don't interact without some medium.
It is possible for very high power beams to effect each other but this is a fairly small effect and wouldn't creae a glowing point of light.

Staff: Mentor

The effect shown there, and the only effect that I know of to create a glowing spot in mid-air, is through focusing of a powerful laser down to a point so that the electric field at that point is high enough to ionize the air and cause it to glow or spark.

I saw it demonstrated at a laser trade show many years ago, where they had a wide beam laser focused to a spot (inside a protective plastic enclosure). It was a pulsed beam (maybe CO2 laser?), which fired about once a second. Pretty impressive spark at the focul point.

Staff: Mentor

Yeah, it fits the definition. But as you said in your post, that's not an optical-optical double resonance (OODR) non-linear beam interaction effect. It's just like focusing sunlight with a magnifying glass on a piece of paper... not that I ever did that as a kid...

No - light beams at sensible powers don't interact without some medium.

Most curious. Does that mean the if one splits a coherent light source into two seperate streams and then via mirrors causes them to intersect with each other at, say, right angles that regardless of the phase of the two beams (make one of the mirrors movable to adjust the phase of one of the beams) that both beams pass through one another unaffected?

It's just like focusing sunlight with a magnifying glass on a piece of paper... not that I ever did that as a kid...

magnifying glasses are for amateurs - 'somebody' forgot that the 10m Keck telescope doesn't have a mirror cover - it just parks facing the horizon to keep dust off, they opened the dome to acclimatise it and forgot to face the telescope away from the setting sun......
Fortunately they noticed before the instrument melted.

Awesome! Regardless of whether the beam is treated as a wave or a particle or both, it cannot be configured to create interference with itself? Dare one ask if it can create interferences with other coherent sources of different frequencies? I should expect not, but I just want to cover the bases....

While I'm at it may I ask does narrowing or widening, by lenses, alter this principle at all? I mean other than losses to the lens material itself of course.

Staff: Mentor

Awesome! Regardless of whether the beam is treated as a wave or a particle or both, it cannot be configured to create interference with itself? Dare one ask if it can create interferences with other coherent sources of different frequencies? I should expect not, but I just want to cover the bases....

While I'm at it may I ask does narrowing or widening, by lenses, alter this principle at all? I mean other than losses to the lens material itself of course.

Staff: Mentor

Umm, one relates to how a thing relates to another thing of the same force type, say amplitute in waves, the other is about how the fundamental forces um, interact?

Could be wrong, but...you know. But thanks for pointing out the loose language I used berkman.

In the context of this thread, interference would be something like an interference pattern where the beams cross -- a pattern of nodes and anti-nodes of electric field variation as the EM waves of the two coherent beams crossed. You detect it by putting a card or something at the crossing point, and observe the light and dark lines of the interference pattern. The beams are not doing anything to each other, but they change the detected light pattern if both are present (as opposed to only one or the other).

For them to interact, they would need to be quite strong as mgb_phys has said, and they would need to cross in a non-linear optic medium. That's a medium that changes its refraction coefficient as a function of how strong the electric field is locally, so the strong electric field of the EM from one beam chages how the second beam is refracted as they cross. Most optical media are linear (the optical characteristics do not change with the intensity of the light going through them), but a few have some useful non-linearities: